This application claims the benefit of Korean Application No. 98-8644, filed Mar. 14, 1998 in the Korean Patent Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a compatible optical pick-up apparatus for recording and reproducing information from recording media having various formats, and more particularly, the present invention relates to an optical pickup apparatus for recording and reproducing information from recording media using light sources to emit light beams having different wavelengths corresponding to the recording media of the various formats.
2. Description of the Related Art
An optical pick-up apparatus employed in a compact disk player (CDP), a digital versatile disk player (DVDP), a CD-ROM driver or a DVD-ROM driver, records and/or reproduces information on or from a recording medium in a non-contact manner. The recording medium has a standardized size, so that an increase in the information recording density with respect to a recording layer of a predetermined size is required, for which much research is currently being conducted.
A digital versatile disk (DVD) or a high density DVD (HD-DVD) is a high capacity disk that is capable of recording a large amount of information. The DVD has a standardized thickness that differs from the thickness of CD related devices, such as a compact disk (CD), a CD-recordable (CD-R) medium, a CD-I, and a CD-G, with reference to an allowable error of a mechanical disk gradient and a numerical aperture of an object lens.
For example, the numerical aperture of the object lens of the optical pick-up apparatus for recording and/or reproducing information on and from the CD is 0.45, while the numerical aperture of the optical pick-up apparatus for recording and/or reproducing information on and from the DVD is 0.6, in order to increase the recording and reproduction density. Due to an allowable error of the mechanical disk gradient that results from using an object lens having large numerical apertures, the thickness of the CD is 1.2 mm, and the thickness of the DVD is 0.6 mm. In the same way, the thickness of the HD-DVD also will be standardized to 0.6 mm.
Furthermore, wavelengths of the reproducing light sources used for the DVD are different from those used for the CD. For example, the wavelength of a light source for reproducing information from a conventional CD is approximately 780 nm, while the wavelength of a light source for reproducing information from a conventional DVD is in a range from approximately 635 nm to 650 nm. A light source emitting light beams of a shorter wavelength in a range from approximately 410 nm to 420 nm is used when reproducing information from the HD-DVD.
The thicknesses of the CD and DVD differ so that if information is recorded and/or reproduced on and from the CD by an optical pick-up apparatus for a DVD, a spherical aberration is generated due to the difference in the thicknesses. Therefore, the optical intensity required to record the information cannot be obtained, or the reproducing signal deteriorates.
A compatible optical pick-up apparatus for a DVD that is capable of reproducing information from a CD includes a light source that emits a light beam that has a wavelength of approximately 650 nm, a beam splitter for directing incident light beams, an object lens for converging a light beam to form a light spot on a recording surface of a disk, and a photodetector for detecting an error signal and an information signal. In this case, the numerical aperture of the object lens is 0.6.
If an object lens, in which an annular optical control pattern is formed, is employed, the spherical aberration caused by the difference in the thicknesses of the disks can be compensated for, to thereby compatibly employ disks having different thicknesses.
In other words, the optical pick-up apparatus includes a light source for the DVD and means capable of compensating for the difference in thicknesses of employed disks, to thereby allow CD reproduction. When reproducing information from the CD, deterioration of approximately 5% is generated, compared to an optical pick-up apparatus employing a light source for a CD emitting light beams that have a wavelength of 780 nm, which is within a range of a reproducing allowable error.
However, if a CD related device, such as a CD-R is employed, along with light sources that have wavelengths of 650 nm and 780 nm, sensitivities are different from each other. For example, the CD-R includes a recording layer of an organic pigment film, so that a difference in reflectivities in accordance with wavelengths of light is great. As a result, the reflectivity is high when using light beams that have a wavelength of 780 nm, while the reflectivity deteriorates to 10% or less when using light beams that have a wavelength of approximately 650 nm, to thereby reproduce no information.
In addition, in the optical pick-up apparatus for the HD-DVD that employs a light source emitting light beams that have a wavelength of approximately 410 nm, recording and reproduction with respect to a CD-R and an expected DVD-R is not possible.
It is an object of the present invention to provide a compatible optical pick-up apparatus allowing recording media having various formats to have information recorded thereon and reproduced therefrom.
Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Accordingly, to achieve the above and other objects of the present invention, there is provided an optical pick-up apparatus for recording and reproducing information from first, second, and third recording media. A first light source emits a light beam that has a wavelength corresponding to the first recording medium, a second light source emits a light beam that has a wavelength corresponding to the second recording medium, and a third light source emits a light beam that has a wavelength corresponding to the third recording medium. A dichroic beam splitter has a first input surface, a second input surface, and a third input surface to receive the light beams emitted from the first, the second and the third light sources, respectively, and an output surface through which the light beams received by the first, the second, and the third input surfaces are transmitted toward the first, the second, and the third recording media, respectively. A converging device converges the light beams transmitted through the output surface of the dichroic beam splitter toward the first, the second, and the third recording media, respectively, and photodetectors receive the light beams reflected from the first, the second, and the third recording media, respectively.
The dichroic beam splitter has a first slant reflection surface to transmit the light beam output from the first light source and to reflect the light beam output from the second light source toward the output surface, and a second slant reflection surface to transmit the light beam output from the first light source and to reflect the light beam emitted from the third light source toward the output surface. The first and the second slant reflection surfaces are formed by alternately repeatedly stacking dielectric layers having different refractivities, and the dielectric layers are preferably alternately formed of MgF2 and TiO2, SiO2 and ZrO2, Al2O3 and ZrO2, MgF2 and ZrO2, SiO2 and TiO2, or Al2O3 and TiO2,
Objects of the invention are also achieved by providing an optical pick-up apparatus for recording and reproducing information from first and second recording media that includes a first light source and a second light source to emit light beams that have wavelengths corresponding to the first and second recording media. A dichroic beam splitter has input surfaces to receive the light beams emitted from the first and the second light sources, and an output surface through which the light beams received by the input surfaces are transmitted toward the first and the second recording media, respectively. A converging device converges the light beams transmitted through the output surface of the dichroic beam splitter to the first and the second recording media, respectively, and photodetectors receive the light beams reflected from the first and the second recording media, respectively.